1. Field of the Invention
The present invention relates to a device for converting a mechanical displacement into an electric signal. More particularly, it relates to a displacement - electricity transducer which can simply detect a displacement at a very high sensitivity over a long term of use even where, as in the throttle valve of an automobile, a transport plane, or the like, the angular displacement is large and service temperature conditions are severe.
2. Description of the Prior Art
In recent years, with the growth of the automobile industry, the exhaust gas emitted from the automobile engine has caused a serious social problem as a source of environmental hazards. Therefore, a tendency has been seen to control the exhaust gas by any method such as a catalytic method. Regulation by legislation has also been considered in earnest. As a radical expedient, however, the development of a clean engine is necessary. It is believed the first essential to make the exhaust gas clean is to control the combustion within the engine.
To this end, a variety of engines are being developed and put into practical use as "clean" engines. These engines are not perfect, however. In order that the combustion explosion itself may be controlled so as to always keep the exhaust gas perfectly clean, it is necessary to further adopt a centralized control system based on an electronic circuit including a mini-computer.
That is, the prime aim of the future auto development will be to make it possible that all the sections of an automobile are electronically subject to centralized automatic control. In order to maintain the engine in the optimum state as a part of the means for achieving the aim, there has been a strong demand for an electronic detector which monitors and controls fuel injection and the air intake controller of the engine. In other words, there has been a strong demand for a device which precisely detects the displacement of the throttle valve for regulating the fuel and air quantities in the automobile engine.
Automobiles are used over extensive regions from cold to tropical climates. Further, the difference between temperatures at starting and at a steady running of the engine is large, and the service temperature range is as wide as from -40.degree. C. to +120.degree. C. The conditions of the service environment are naturally extremely severe irrespective of bad roads, dust, rain, snow etc. Accordingly, the displacement detector for automobile engines must be a structure which satisfactorily takes the thermal resistance, vibration resistance, moisture resistance corrosion resistance etc. into consideration and must simultaneously be a structure which is capable of a high sensitivity detection of the displacement. Moreover, the displacement detector must be structurally simple in order to be inexpensive in production and must be durable in order to repeatedly detect, for several million times, the displacements which vary frequently on account of use.
As a principal device of the displacement - electricity transducer fulfilling the above requisites, a variable inductor has been proposed which comprises a movable magnetic core and a fixed magnetic core oppositely arranged so as to have prescribed gaps in at least two places, both magnetic cores substantially forming two magnetic circuits each including one gap, coils being wound around parts of the respective magnetic circuits, so that when the movable magnetic core is relatively displaced, while being held at a predetermined spacing with respect to the fixed magnetic core, the substantially opposite area of the gap portion in one magnetic circuit increases, while the substantially opposite area of the gap portion in the other magnetic circuit decreases. (copending U.S. Pat. application Ser. No. 485,626, commonly assigned).
In the variable inductor, however, the magnetic reluctance of the magnetic core is not perfectly negligible in comparison with that of the gap, and the exciting coil is wound around a part not common to the two magnetic paths. For these reasons, a third magnetic path, other than the two magnetic paths, is formed, and mutual induction between the respective magnetic path arises, and, although slight is a problem.